Cell surface receptors, ion channels, and transporters are critical components of signaling and excitability in the nervous system. As such, they represent the majority of drug targets currently being explored in the pharmaceutical industry. Basic studies have revealed that these proteins are nonuniformly distributed on neurons and targets and this distribution can be impacted by multiple signal transduction pathways and endogenous regulatory programs. Moreover, many drugs appear to alter the responsiveness, distribution and/or surface abundance of their protein targets following chronic occupancy. Currently, the detection, quantitation and localintion of membrane proteins is achieved largely using radiolabeled ligands or indirectly with antibody techniques. These approaches are limited due to the poor spatial resolution of radiotracer studies, the limited availability of surface domain-selective antibody probes for membrane proteins, the broad emission spectra of available fluorophores and their photochemical degradation. In this proposal we will continue to develop our novel, non-isotopic, labeling strategies with a principal focus on drug-conjugated fluorescent nanocrystals (nanoconjugates) that can permit the imaging and quantitative analysis of cell surface receptor and transporter proteins. Specifically we will: I. Synthesize improved nanocrystal probes. II. Establish dynamic imaging of the serotonin transporter protein. III. Develop pharmacological assays that exploit the unique properties of drug-conjugated nanocrystals. To accomplish these aims we have assembled an interdisciplinary team of chemists, microscopists, pharmacologists and neuroscientists. The experiments proposed here exploit the unique optical properties of fluorescent nanocrystals and cannot be performed with traditional organic fluorophores or fluorescent proteins. In this proposal nanotechnology interfaces with neuroscience in a way that advances both fields.